Both Lopez's and the victim's families were present. Lopez waived his right to speak at trial.
Police say Lopez went to South East High School during lunchtime on Friday. After an argument between his ex-girlfriend Cindi Santa, 17, he beat and stabbed Santana several times. She died at St. Francis Medical Center Friday night.
Prosecutors allege that three other victims were also stabbed in the incident, including another student and a female dean. They also say that Lopez threatened three police officers by waving a knife at them.
Lopez was a student at South East High School, but had not been seen on campus since he was arrested on Sept. 25 for making a criminal threat against Santana. Authorities said he sent text messages saying that he was going to send men to beat up her sister's husband.
The district attorney's office did not press charges due to insufficient evidence and Lopez was released from jail two days later.
Lopez's mother, Elizabeth Mendiola, was in the courtroom Tuesday.
"My condolences go out to her family. It's really devastating what's going on," said Mendiola.
"I'm totally shocked because that is not my son," said Mendiola. "He had his mind set on a great future being a police officer, finishing school, getting married with her, having a family with her, and I just don't understand what happened."
Friends of Lopez's were at court Tuesday to support him.
"We knew the person he was, who he still is, before he made this mistake. We know who he is. This is not who he is," said Catherine Pacheco, a friend of Lopez's.
Lopez is charged with 10 felonies, including one count each of first-degree murder and false imprisonment by violence, and three counts of assault with a deadly weapon. Lopez was held on $1.2 million bail.
Prosecutors will likely be seeking life in prison with the possibility of parole. His next court appearance is Oct. 25.